Use the event name in methods like addEventListener(), or set an event handler property.

addEventListener("unhandledrejection", (event) => {});
onunhandledrejection = (event) => {};

A Event.

PromiseRejectionEvent.promise Read only

The JavaScript Promise that was rejected.

PromiseRejectionEvent.reason Read only

A value or Promise.reject().

In addition to the Window interface, the event handler property onunhandledrejection is also available on the following targets:

• HTMLBodyElement
• HTMLFrameSetElement
• SVGSVGElement

Allowing the unhandledrejection event to bubble will eventually result in an error message being output to the console. You can prevent this by calling PromiseRejectionEvent; see Preventing default handling below for an example.

Because this event can leak data, Promise rejections that originate from a cross-origin script won't fire this event.

This example logs information about the unhandled promise rejection to the console.

window.addEventListener("unhandledrejection", (event) => {
  console.warn(`UNHANDLED PROMISE REJECTION: ${event.reason}`);
});

You can also use the onunhandledrejection event handler property to set up the event listener:

window.onunhandledrejection = (event) => {
  console.warn(`UNHANDLED PROMISE REJECTION: ${event.reason}`);
};

Many environments (such as preventDefault() to cancel the event, preventing it from bubbling up to be handled by the runtime's logging code. This works because unhandledrejection is cancelable.

window.addEventListener("unhandledrejection", (event) => {
  / code for handling the unhandled rejection
  / …

  / Prevent the default handling (such as outputting the
  / error to the console)

  event.preventDefault();
});

• Promise rejection events
• rejectionhandled event
• Promise